1. Field of the Invention
The present invention relates to a sheet stacking apparatus used in fax machines, copying machines, printers, and multifunction machines combining the functions thereof, and an image forming apparatus including the sheet stacking apparatus.
2. Description of the Related Art
Recently, it has become increasingly necessary to miniaturize the apparatus main body of an image forming apparatus of fax machines, copying machines, printers, and multifunction machines combining the functions thereof. For example, in order to avoid increasing the footprint of the apparatus, a sheet stacking portion which stacks discharged sheets on which an image is formed and discharged original copies from which an image is read is provided above the apparatus main body. Further, an image forming apparatus in which an image reading portion which reads the image of an original copy is provided above the sheet stacking portion is known, as well as one having an upper unit such as an upper level sheet stacking portion among a plurality of sheet stacking portions.
In this kind of apparatus, as a further method for miniaturizing the apparatus main body, the size of a sheet stacking space including the top surface of the sheet stacking portion and the lower surface of the upper unit can be reduced.
In an apparatus in which the size of the sheet stacking space has been reduced, in order to secure a certain amount of sheet stacking, a sheet pressing lever which presses down any bulging of the stacked sheets can be provided. Alternatively, in order to prevent overstacking of the sheets, a member which detects the amount of sheet stacking via a stacking amount detection lever can be provided. In general, a sheet pressing lever or a stacking amount detection lever is provided so that it can rotate in the up-down direction, which is the stacking direction of the sheets, and the lever is held at a lower limit position of a movement region in which the lever can rotate by a regulation portion which regulates the rotation of the lever.
Therefore, as a lever breakage prevention portion for when a force is applied in a direction which makes the lever rotate even lower than the lower limit position of the movement region, Japanese Patent Application Laid-Open No. 2003-300661 discloses arranging a spring member on a regulation portion which regulates the lower limit position of rotation of a stacking amount detection lever. Thereby, when a force is applied in a direction which makes the lever rotate even lower than the lower limit position in a state in which the upper unit is closed, the regulation portion is displaced by the elasticity of the spring member and the top surface of the sheet stacking portion regulates the rotation of the lever, thus breakage of the stacking detection lever is avoided.
However, in a state in which the upper unit is opened upward, the space from the rotating edge of the lever to the top surface of the sheet stacking portion is larger than that in the state in which the upper unit is closed, and thus the rotation of the lever cannot be regulated at the top surface of the sheet stacking portion. In a state in which the upper unit is opened, even if the technology disclosed in Japanese Patent Application Laid-Open No. 2003-300661 is used, since there are limits to the elasticity displacement magnitude (rotation range) of the lever by the spring member, the lever may break if a force exceeding the rotation range is applied to the lever.
The present invention provides a sheet stacking apparatus in which a lever held in a lower limit position will not break even if a force is applied in a direction which makes the lever rotate even lower than the lower limit position, and the back action of the lever can be reduced even if the force is released.